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MG Midget and Sprite Technical - Filling the centre main casting window with epoxy

Most 1275 midget thick-flange blocks (?all but 73-74 engines with 788 in their number) have a 'casting window' - a ragged hole - above the centre main bearing, which may compromise its strength. Why not, after having had the block caustic dipped, fill up the casting hole with epoxy?

One problem I can envisage is that cast iron absorbs oil, which may not be wholly removed by the caustic dip, meaning the epoxy won't stick. 'Cooking' the block and applying solvents may be necessary. However, if the epoxy did come loose, it's not going to go anywhere because the jagged edges of the casting window will retain it. Even if it fell out, it would only drop into the sump without doing any harm.

The question is, would it do any good? Metal-filled epoxies are being used for evermore adventurous repairs, it seems - and iron-filled ones are available, so its expansion coefficient would match that of the block - it could perhaps provide real extra support for the centre main. At the very least, the epoxy could damp out some of the stresses caused by the sharp edges of the window.

Is this one of those early-hours-of-the-morning notions that evaporate in the light of day? What have I not though of? I would be very interested in BBSers' opinions.

Tom
Tom Coulthard

Tom
I dont believe filling the hole with epoxy would do any good.
Its probably better the grind the hole to a smooth finish to remove any sharp/jagged edges that could be potential stress risers. Also do the same thing anywhere else inside the crankcase for the same reason.
Ian.
Ian Webb '73 GAN5

<<and iron-filled ones are available, so its expansion coefficient would match that of the block >>
I don't think that would be the case. The plug of epoxy will almost certainly not stay where you put it for very long, especially given where it is and the environment it is suffering!
David Cox

I can't see anything that would be gained by having a do at it. The epoxy would need to be 100% iron to match the expansion co-efficient of the block, which no longer makes it an epoxy, but just iron. And if it did drop out, which I think it eventually would, it would only stay in one piece for a few moments and then you'd have lots of little bits floating round the engine. The con rods and crank would smash it up in no time.

I can see where you're coming from with the idea, but as said, you would be better off grinding the area smooth to remove any stress raisers. The only other thing I can think of that would maybe help would be to fit something like the 4 bolt centre main cap, but the cost and time involved would, I expect, make such a venture a total waste of time for anything other than a race engine.
S Overy

With the grind smooth camp here.
Actualy i am in the proces of preping a thick flange block.
And the next thing on my list is grinding all that is jaged smooth.
Thoug that is mostly the casting window and some small edges.
Not going to a mirror finish just a coarse 80 grit grind.

To bad my thin flange block is cracked.
As i think the disatvantage of the thinner flange is more than made up by not having a hole above your center main bearing
Onno Könemann

what's the evidence that the casting hole causes any problem? It might be more effective to have the bottom end balanced to a finer degree - when did any of us actaully ask the tolerance that it's balanced to? How do you measure the balance (or imbalance) in a crank assembly anyway? And in what units?
David Smith

Tom
Better off going back to sleep and thinking of something else like a nice juicey steak or a speedboat or something Willy
William Revit

William,

Your comment reminds me of "Eats, shoots, and leaves", I presume you meant to have a full stop (period to those in the US) at the end of your comment.
David Billington

reckon a ',' comma between the last 'something' and 'Willy' would stop me having unwanted dreams!
MarkDJ-glos

how big is the hole?

If not to big, maybe grind it out smooth and put a bolt/stud thur it an weld it in place... just an idea


If you do go the epoxy way... the 2 best epoxys ive found of the JB weld version are called... Loctite and permaweld ... I like the loctite weld the best, it sets up faster about 5-10 minutes, but if you need alot of time to tool the epoxy... say 20 minutes to 1/2 hour the permaweld is best

DO NOT USE the fast setting epoxys, you want the LOOOONNNGGGGGG setting stuff, The stuff that takes along time to cure lives up to its name and is vary permante (provided you have the patiance)... Im a growing fan of these epoxy welds, esp for body work for foinging sheet metal...

its come along way scence the days of JB weld... If you use the fast setting stuff, you might as well use play dough... its just to brittle and has no bonding strength to be useful on vary many applications

Prop
Prop

Ah---------Sorry to keep you awake guys-------------------------------------------------------------------Willy
William Revit

now this is fun the all knowing Prop does not know how the casting window on an A-series looks like!!
Onno Könemann

David -

Is this evidence?

To be honest, this came out of a race engine that a friend got when he bought his car, so I don't know what sort of abuse this block may have received. Also, I have seen 948s that have done similar, and they have no window, but they do rev up to 10K rpm.

I don't think I would want to rely on epoxy staying put. I generally spend some quality time with the block and a grinder, smoothing lumps and rough edges, not getting too fussy. I had a couple of good balance shops do my balancing - no idea of their tolerances, but one did a lot of industrial balancing, including large computer disk drives, and the other did a lot of motorcycle race engines, so both knew about high revs.

- Bill

Bill Gavin

To be really honest Onno...

I didnt have any holes/windows in the center main castings, so I am at a disadvantage... the only hole I had like this was on the front of the block just behind the timing chain, I used a rat tail file and dia grinder to smooth it out before going to the machine shop

just a little clarity... I too would not use the epoxy on this window in the block, my comentary was just my opinion on which 2 part epoxys are the best in terms of general usage, having used alot of differant brands over the past decade or so... as I said, I do like them for certian applications and if you were going to use an epoxy for this hole... those 2 epoxys I mentioned earlyer would be your BEST shot at success... In my opinion
Prop

Tom
Whilst I dont agree with doing it, if the correct industrial quality of epoxy was used and it was applied corectly I think it would stay in position.

I have seen it used successfully on much higher revving prototype/development engines for similar things.
Ian
Ian Webb '73 GAN5

whoops...

I didn't attach the photo!

- Bill


Bill Gavin

Bill

WHOOPS ???

I think epoxy would be over kill, super glue might work better...LOL

Where you driving that engine when that happened.... Dam* thats insane... Ive never seen or heard of that happening before

Thats a photo of a bad day

Prop
Prop

That engine came out of a friend's race car many years ago. After a long string of DNFs we eventually convinced him to rebuild the car from the ground up. In his first year of racing Nationals, he qualified for the Runoffs at Road Atlanta - back when that meant something.

That block ended up in my garage after we got the car sorted out: I eventually recycled the block, but had to keep the center main :-)

After many years of racing, I've seen quite a variety of failures - fortunately, very few were my own :-)

- Bill
Bill Gavin

Many thanks to all who have posted on this topic - very interesting. Before taking up any individual points, I thought I'd better just put up some pics so that people know what we're on about. The first is taken through the front main bearing ...


Tom Coulthard

The second is the same engine (which is 'upside down') taken from a higher angle:


Tom Coulthard

This is another engine:


Tom Coulthard

And finally a third engine showing that cast 'oles are unlike other things in life, in that though they're all different, we don't all have one ...


Tom Coulthard

This thread was discussed between 04/02/2011 and 08/02/2011

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This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.